The present invention relates to a whirlpool bath with an inverter-controlled circulating pump.
For giving a massaging effect to a bather, there has been provided a whirlpool bath unit which injects air-incorporated water into a bathtub. This known whirlpool bath unit comprises a bathtub, a circulating pump disposed separate from the bathtub, a return passage having one end connected to the circulating pump and the other end opening into the bathtub, a return passage having one end connected to the circulating pump and the other end opening into the bathtub, a water injection passage having one end connected to the circulating pump and the other end connected to branch passages opening into the bathtub, and an air-mixing unit connected to the water injection passage to mix air into the water flowing through the water injection passage.
Recently, as one of the improvements on such whirlpool bath unit, a whirlpool bath employing an inverter to drive the motor of the circulating pump has been proposed in Japanese laid-open utility model application 63-100035, wherein the rate of revolution of the motor is varied smoothly by the inverter to control the discharge pressure and discharge rate of the blow-off water.
The AC output of the inverter, however, includes very substantial high-frequency components as shown in FIGS. 51 and 52 The high-frequency components leak into the field core due to the capacitive coupling of the field core and winding of the motor. When the motor is not grounded perfectly, there is the danger of a bathing person bathing in the bathtub being struck by the leakage of high-frequency components that flow through the circulating pump into the water contained in the bathtub. Since one of the conductors of a commercial power source is grounded without exception, the bathing person may possibly be struck by a high-frequency current generated by the inverter when the bathing person touches a grounded part of the whirlpool bath unit, because the high-frequency current flows through the following circuit: the inverter.fwdarw.the winding of the motor.fwdarw.(capacitive coupling).fwdarw.the field core of the motor.fwdarw.the circulating pump.fwdarw.water.fwdarw.bathing person.fwdarw.the grounded part of the ground.fwdarw.the grounded line of the commercial power source.fwdarw.lines connecting the commercial power source to the inverter.fwdarw.the inverter.
If the inverter and the circulating pump are connected electrically by a case or the like, the bathing person is struck by a high-frequency current generated by the inverter that flows through the following circuit: the inverter.fwdarw.the case.fwdarw.the circulating pump.fwdarw.water.fwdarw.the bathing person.fwdarw.the grounded part.fwdarw.the ground.fwdarw.the grounded line of the commercial power source.fwdarw.lines connecting the commercial source to the inverter.fwdarw.the inverter.
Accordingly, it is an object of this invention to provide a whirlpool bath which can resolve such problems.